The homeostasis of the muco-ciliary epithelium lining the airways is frequently disrupted by microbial and chemical agents contaminating the ambient air. The accompanying inflammation causes marked changes in airway secretions and disruption or loss of differentiation. The biochemical and molecular events occurring as a result of airway injury and during the subsequent regeneration and redifferentiation are poorly understood. The main objectives of these investigations are: 1) To determine which factors are critical in regulating mucin and non-mucin airway secretions and to elucidate the mechanisms involved. 2) To elucidate factors and mechanisms controlling ciliagenesis and ciliated cell differentiation. 3) To characterize specific biochemical and molecular events occurring during airway inflammation and define the role the airway epithelium itself plays in the pathogenesis of airway inflammation. Regulation of airway secretions. To obtain probes to study the expression and functions of mucins in an in vitro model of airway cell differentiation and disease the rat cDNA homologue of the human airway secretory mucin, MUC5 was isolated and characterized. The coordinate regulation of expression of MUC5 and MUC1 (a membrane bound mucin) and mucous differentiation was demonstrated in cultured rat tracheal cells using a monoclonal antibody reacting with mucous cells and their secretions. The rat MUC5 was cloned by RT-PCR using motifs conserved in the human secretory mucins MUC2 and MUC5. The rat cDNA revealed a high degree of sequence similarity to human MUC5, 73% homology at the amino acid level. The regulation of mucin gene expression, mucin secretion and mucous cell differentiation by retinoids and EGF is being investigated. Regulation of ciliated cell differentiation. Several factors regulating ciliated cell differentiation were identified: EGF, choleratoxin and hydrocortisone. To investigate molecular mechanisms of ciliagenesis degenerate primers to conserved regions of known paramecium axonemal dynein heavy chains were used to identify and clone 7 unique axonemal dynein heavy chains from rat tracheal epithelium. Northern analysis of RNA from rat tracheal cells showed a single transcript of ~15kb. Expression of these genes was restricted to tissues containing axonemes (trachea, testis, brain). Factors which regulate the development of ciliated cells regulated the expression of axonemal dyneins in a parallel fashion. These are the first mammalian dynein heavy chain genes shown to be specifically expressed in axonemal tissues. future studies will be directed at identifying mechanisms which regulate the differentiation specific expression of dynein heavy chains.